Showing papers on "Electric potential published in 2006"

Piezoelectric and semiconducting coupled power generating process of a single ZnO belt/wire. A technology for harvesting electricity from the environment.

Abstract: This paper presents the experimental observation of piezoelectric generation from a single ZnO wire/belt for illustrating a fundamental process of converting mechanical energy into electricity at nanoscale. By deflecting a wire/belt using a conductive atomic force microscope tip in contact mode, the energy is first created by the deflection force and stored by piezoelectric potential, and later converts into piezoelectric energy. The mechanism of the generator is a result of coupled semiconducting and piezoelectric properties of ZnO. A piezoelectric effect is required to create electric potential of ionic charges from elastic deformation; semiconducting property is necessary to separate and maintain the charges and then release the potential via the rectifying behavior of the Schottky barrier at the metal-ZnO interface, which serves as a switch in the entire process. The good conductivity of ZnO is rather unique because it makes the current flow possible. This paper demonstrates a principle for harvesting energy from the environment. The technology has the potential of converting mechanical movement energy (such as body movement, muscle stretching, blood pressure), vibration energy (such as acoustic/ultrasonic wave), and hydraulic energy (such as flow of body fluid, blood flow, contraction of blood vessels) into electric energy that may be sufficient for self-powering nanodevices and nanosystems in applications such as in situ, real-time, and implantable biosensing, biomedical monitoring, and biodetection.

Magnetic and electric phase control in epitaxial EuTiO(3) from first principles.

Abstract: We propose a design strategy---based on the coupling of spins, optical phonons, and strain---for systems in which magnetic (electric) phase control can be achieved by an applied electric (magnetic) field. Using first-principles density-functional theory calculations, we present a realization of this strategy for the magnetic perovskite ${\mathrm{EuTiO}}_{3}$.

Using Self‐Assembling Dipole Molecules to Improve Charge Collection in Molecular Solar Cells

Abstract: Surface modification of indium tin oxide (ITO)-coated substrates through the use of self-assembled monolayers (SAMs) of molecules with permanent dipole moments has been used to control the anode work function and device performance in molecular solar cells based on a CuPc:C60 (CuPc: copper phthalocyanine) heterojunction. Use of SAMs increases both the short-circuit current density (Jsc) and fill factor, increasing the power-conversion efficiency by up to an order of magnitude. This improvement is attributed primarily to an enhanced interfacial charge transfer rate at the anode, due to both a decrease in the interfacial energy step between the anode work function and the highest occupied molecular orbital (HOMO) level of the organic layer, and a better compatibility of the SAM-modified electrodes with the initial CuPc layers, which leads to a higher density of active sites for charge transfer. An additional factor may be the influence of increasing electric field at the heterojunction on the exciton-dissociation efficiency. This is supported by calculations of the electric potential distribution for the structures. Work-function modification has virtually no effect on the open-circuit voltage (Voc), in accordance with the idea that Voc is controlled primarily by the energy levels of the donor and acceptor materials.

Electric field control of spin transport

Abstract: Spintronics aims to develop electronic devices whose resistance is controlled by the spin of the charge carriers that flow through them1,2,3. This approach is illustrated by the operation of the most basic spintronic device, the spin valve4,5,6, which can be formed if two ferromagnetic electrodes are separated by a thin tunnelling barrier. In most cases, its resistance is greater when the two electrodes are magnetized in opposite directions than when they are magnetized in the same direction7,8. The relative difference in resistance, the so-called magnetoresistance, is then positive. However, if the transport of carriers inside the device is spin- or energy-dependent3, the opposite can occur and the magnetoresistance is negative9. The next step is to construct an analogous device to a field-effect transistor by using this effect to control spin transport and magnetoresistance with a voltage applied to a gate10,11. In practice though, implementing such a device has proved difficult. Here, we report on a pronounced gate-field-controlled magnetoresistance response in carbon nanotubes connected by ferromagnetic leads. Both the magnitude and the sign of the magnetoresistance in the resulting devices can be tuned in a predictable manner. This opens an important route to the realization of multifunctional spintronic devices.

Nonlinear screening of charge impurities in graphene

Abstract: It is shown that a ``vacuum polarization'' induced by Coulomb potential in graphene leads to a strong suppression of electric charges even for undoped case (no charge carriers). A standard linear response theory is therefore not applicable to describe the screening of charge impurities in graphene. In particular, it overestimates essentially the contributions of charge impurities into the resistivity of graphene.

Space-charge-limited flows in the quantum regime

Abstract: This paper reviews the recent developments of space-charge-limited (SCL) flow or Child-Langmuir (CL) law in the quantum regime. According to the classical CL law for planar diodes, the current density scales as 3∕2’s power of gap voltage and to the inverse squared power of gap spacing. When the electron de Broglie wavelength is comparable or larger than the gap spacing, the classical SCL current density is enhanced by a large factor due to electron tunneling and exchange-correlation effects, and there is a new quantum scaling for the current density, which is proportional to the 1∕2’s power of gap voltage, and to the inverse fourth-power of gap spacing. It is also found that the classical concepts of the SCL flow such as bipolar flow, transit time, beam-loaded capacitance, emitted charge density, and magnetic insulation are no longer valid in quantum regime. In the quantum regime, there exists a minimum transit time of the SCL flows, in contrast to the classical solution. By including the surface properties of the emitting surface, there is a threshold voltage that is required to obtain the quantum CL law. The implications of the Fowler-Nordheim-like field emission in the presence of intense space charge over the nanometer scale is discussed.

Determining a magnetic Schroedinger operator from partial Cauchy data

Abstract: In this paper we show, in dimension n >=3, that knowledge of the Cauchy data for the Schroedinger equation in the presence of a magnetic potential, measured on possibly very small subsets of the boundary, determines uniquely the magnetic field and the electric potential.

Schwinger pair production in electric and magnetic fields

Abstract: Charged particles in static electric and magnetic fields have Landau levels and tunneling states from the vacuum. Using the instanton method of Phys. Rev. D 65, 105002 (2002), we obtain the formulas for the pair-production rate in spinor and scalar QED, which sum over all Landau levels and recover exactly the well-known results. The pair-production rates are calculated for an electric field of finite extent, and for the Sauter potential, both with a constant magnetic field also present, and are shown to have finite-size effects.

DC-dielectrophoretic separation of microparticles using an oil droplet obstacle

Abstract: A new dielectrophoretic particle separation method is demonstrated and examined in the following experimental study. Current electrodeless dielectrophoretic (DEP) separation techniques utilize insulating solid obstacles in a DC or low-frequency AC field, while this novel method employs an oil droplet acting as an insulating hurdle between two electrodes. When particles move in a non-uniform DC field locally formed by the droplet, they are exposed to a negative DEP force linearly dependent on their volume, which allows the particle separation by size. Since the size of the droplet can be dynamically changed, the electric field gradient, and hence DEP force, becomes easily controllable and adjustable to various separation parameters. By adjusting the droplet size, particles of three different diameter sizes, 1 µm, 5.7 µm and 15.7 µm, were successfully separated in a PDMS microfluidic chip, under applied field strength in the range from 80 V cm−1 to 240 V cm−1. A very effective separation was realized at the low field strength, since the electric field gradient was proved to be a more significant parameter for particle discrimination than the applied voltage. By utilizing low strength fields and adaptable field gradient, this method can also be applied to the separation of biological samples that are generally very sensitive to high electric potential.

Seismoelectric numerical modeling on a grid

Abstract: Our finite-difference algorithm provides a new method for simulating how seismic waves in arbitrarily heterogeneous porous media generate electric fields through an electrokinetic mechanism called seismoelectric coupling. As the first step in our simulations, we calculate relative pore-fluid/grain-matrix displacement by using existing poroelastic theory. We then calculate the electric current resulting from the grain/fluid displacement by using seismoelectric coupling theory. This electrofiltration current acts as a source term in Poisson’s equation, which then allows us to calculate the electric potential distribution. We can safely neglect induction effects in our simulations because the model area is within the electrostatic near field for the depth of investigation (tens to hundreds of meters) and the frequency ranges ( 10 Hz to 1 kHz ) of interest for shallow seismoelectric surveys.We can independently calculate the electric-potential distribution for each time step in the poroelastic simulation with...

Semiclassical Pseudodifferential Calculus and the Reconstruction of a Magnetic Field

Abstract: We give a procedure for reconstructing a magnetic field and electric potential from boundary measurements given by the Dirichlet to Neumann map for the magnetic Schrodinger operator in R n , n ≥ 3. The magnetic potential is assumed to be continuous with L ∞ divergence and zero boundary values. The method is based on semiclassical pseudodifferential calculus and the construction of complex geometrical optics solutions in weighted Sobolev spaces.

Ginzburg-Landau theory of solvation in polar fluids: Ion distribution around an interface

Abstract: We present a Ginzburg-Landau theory of solvation of ions in polar binary mixtures. The solvation free energy arising from the ion-dipole interaction can strongly depend on the composition and the ion species. Most crucial in phase separation is then the difference in the solvation free energy between the two phases, which is the origin of the Galvani potential difference known in electrochemistry. We also take into account an image potential acting on each ion, which arises from inhomogeneity in the dielectric constant and is important close to an interface at very small ion densities. Including these solvation and image interactions, we calculate the ion distributions and the electric potential around an interface with finite thickness. In particular, on approaching the critical point, the ion density difference between the two phases becomes milder. The critical temperature itself is much shifted even by a small amount of ions. We examine the surface tension in the presence of ions in various cases.

Comparison of hybrid Hall thruster model to experimental measurements

Abstract: ** A two -dimensional hybrid particle -in -cell numerical model has been constructed in the radial -axial plane with the intent of examining the physics governing Hall thruster operation. The electrons are treated as a magnetized quasi -one -dimensi onal fluid and the ions are treated as collisionless, nonmagnetized discrete particles. The anomalously high electron conductivity experimentally observed in Hall thrusters is accounted for using experimental measurements in the Stanford Hall thruster. An evaluation is made of differing treatments of electron mobility, background gas, neutral wall interactions, and charge exchange collisions. The results are compared to experimental measurements of ion and neutral number densities and velocities, electron t emperature, and electric potential.

Modeling the electric field of weakly electric fish

Abstract: Weakly electric fish characterize the environment in which they live by sensing distortions in their self-generated electric field. These distortions result in electric images forming across their skin. In order to better understand electric field generation and image formation in one particular species of electric fish, Apteronotus leptorhynchus, we have developed three different numerical models of a two-dimensional cross-section of the fish's body and its surroundings. One of these models mimics the real contour of the fish; two other geometrically simple models allow for an independent study of the effects of the fish's body geometry and conductivity on electric field and image formation. Using these models, we show that the fish's tapered body shape is mainly responsible for the smooth, uniform field in the rostral region, where most electroreceptors are located. The fish's narrowing body geometry is also responsible for the relatively large electric potential in the caudal region. Numerical tests also confirm the previous hypothesis that the electric fish body acts approximately like an ideal voltage divider; this is true especially for the tail region. Next, we calculate electric images produced by simple objects and find they vary according to the current density profile assigned to the fish's electric organ. This explains some of the qualitative differences previously reported for different modeling approaches. The variation of the electric image's shape as a function of different object locations is explained in terms of the fish's geometrical and electrical parameters. Lastly, we discuss novel cues for determining an object's rostro-caudal location and lateral distance using these electric images.

A geometrically non‐linear piezoelectric solid shell element based on a mixed multi‐field variational formulation

Abstract: This paper is concerned with a geometrically non-linear solid shell element to analyse piezoelectric structures. The finite element formulation is based on a variational principle of the Hu-Washizu type and includes six independent fields: displacements, electric potential, strains, electric field, mechanical stresses and dielectric displacements. The element has eight nodes with four nodal degrees of freedoms, three displacements and the electric potential. A bilinear distribution through the thickness of the independent electric field is assumed to fulfill the electric charge conservation law in bending dominated situations exactly. The presented finite shell element is able to model arbitrary curved shell structures and incorporates a 3D-material law. A geometrically non-linear theory allows large deformations and includes stability problems. Linear and non-linear numerical examples demonstrate the ability of the proposed model to analyse piezoelectric devices.

Coulomb and polarization effects in sub-cycle dynamics of strong-field ionization

Abstract: We discuss the sub-cycle dynamics of strong-field ionization by an intense few-cycle laser pulse. Even at high intensities when all the excited states are embedded into the continuum, the dynamics are found to be strongly dependent both on the presence or absence of excited states in the field-free potential and on the structure of the continuum. Both Coulomb effects in the continuum and polarization of the initial state are important even for qualitative description of sub-cycle ionization. We show how to consistently include effects of the binding (Coulomb) potential on the continuum part of the electron wavefunction while retaining the effects of the laser field on the bound part. We demonstrate quantitative accuracy of our approach in the barrier-suppression region of laser intensities.

Numerical simulation of radio frequency ablation with state dependent material parameters in three space dimensions

Abstract: We present a model for the numerical simulation of radio frequency (RF) ablation of tumors with mono- or bipolar probes. This model includes the electrostatic equation and a variant of the well-known bio-heat transfer equation for the distribution of the electric potential and the induced heat. The equations are nonlinearly coupled by material parameters that change with temperature, dehydration and damage of the tissue. A fixed point iteration scheme for the nonlinear model and the spatial discretization with finite elements are presented. Moreover, we incorporate the effect of evaporation of water from the cells at high temperatures using a predictor-corrector like approach. The comparison of the approach to a real ablation concludes the paper.

Electrostatic force microscopy on oriented graphite surfaces: coexistence of insulating and conducting behaviors.

Abstract: We present measurements of the electric potential fluctuations on the surface of highly oriented pyrolytic graphite using electrostatic force and atomic force microscopy. Micrometric domainlike potential distributions are observed even when the sample is grounded. Such potential distributions are unexpected given the good metallic conductivity of graphite because the surface should be an equipotential. Our results indicate the coexistence of regions with "metalliclike" and "insulatinglike" behaviors showing large potential fluctuations of the order of 0.25 V. In lower quality graphite, this effect is not observed. Experiments are performed in Ar and air atmospheres.

Modeling the Potential Distribution in Porous Anodic Alumina Films during Steady-State Growth

Abstract: Porous anodic alumina (PAA) films, formed by anodic oxidation in acidic solutions, contain hexagonal arrays of parallel cylindrical pores, with pore diameter and spacing between ten and several hundred nanometers. Simulations were developed for the electrical potential distribution in the film during steady-state PAA growth, and used to calculate the rates of metal-film and film-solution interface motion. In particular, a model using the assumption of no space charge (Laplace's equation) and one based on the current continuity equation, in each case coupled with high-field ionic conduction, were evaluated with respect to the requirement that the interface profiles are time invariant. Laplace's equation, on which prior simulations of PAA growth were based, yielded unrealistic behavior with highly nonuniform interface motion, suggesting the presence of significant space charge. In contrast, interface motion predicted by the current continuity equation was uniform, except near convex ridges on the metal-film interface between pores. To fully rationalize the steady-state PAA geometry, phenomena other than conduction should be considered, which are able to provide inhibition of the oxidation rate on these ridges.

A Dynamic Mechanistic Model of an Electrochemical Interface

Abstract: We propose a dynamic mechanistic model, based on nonequilibrium thermodynamics and electrodynamics, describing the transient response to current perturbations of an electrochemical double layer at the metal/electrolyte interface in the presence of electrochemical reactions. As an example of application, we have simulated the hydrogen oxidation reaction taking place in a polymer electrolyte fuel cell anode. The model is composed of (i) a 0-D inner layer submodel describing the composition of the metallic phase surface where water and reactant can be adsorbed, and the generated electric potential difference between the metal and the electrolyte phases; and (ii) a 1-D diffuse layer submodel in the electrolyte constituted by spatially moving ions and counterions, describing the ionic transport by migration-diffusion, based on the coupling of a Nernst-Planck's equation with a Poisson's equation. At the interface, the reaction kinetics depending on the potential difference is coupled with the inner-layer model through the charge conservation law. The numerical model allows dynamic simulation of the evolution of the local electric potentials (ionic and electronic) and concentrations inside the interface, and the influence of the working conditions on the impedance spectra characteristics.

Synthesis, characterization and nonlinear optical (NLO) properties of a push–pull bisboronate chromophore with a potential electric field induced NLO switch

Abstract: A new bisboronate with five six-membered ring heterobicycles was prepared by reaction of [2-(2-hydroxy-4-diethylaminobenzylidene)amino]-5-nitroaminophenol and 1,4-phenyldiboronic acid, and its quadratic nonlinear optical (NLO) response was compared to that of a related monoboronate species. A computational investigation conducted within the framework of the DFT theory, at the B3PW91/6-31G* level, indicates that, while the diboronate derivative exhibits a centrosymmetric conformation in the ground state, and hence a vanishing quadratic hyperpolarizability (β), the application of an external electric field provides a gradual intramolecular rotation of the two “push–pull” sub-units which reaches 128° for a field intensity of 10−3 a.u. and leads to a β value equal to 49.2 × 10−30 cm5 esu−1. This result suggests a possibility for a molecular NLO switch induced by an electric field in such systems. Experimentally, the NLO response measured by the electric field induced second harmonic (EFISH) technique indicates an NLO response (expressed as the μ × β product) 1.95 times larger for the bisboronate than for the monoboronate analogue, thus suggesting that, although the ground state conformation is centrosymmetric, the “push–pull” sub-units are in quasi-free rotation at room temperature.

Light-emitting diode and method for fabrication thereof

Abstract: A light-emitting diode includes a substrate, a compound semiconductor layer including a p-n junction-type light-emitting part formed on the substrate, an electric conductor disposed on the compound semiconductor layer and formed of an electrically conductive material optically transparent to the light emitted from the light-emitting part and a high resistance layer possessing higher resistance than the electric conductor and provided in the middle between the compound semiconductor layer and the electric conductor. In the configuration of a light-emitting diode lamp, the electric conductor and the electrode disposed on the semiconductor layer on the side opposite to the electric conductor across the light-emitting layer are made to assume an equal electric potential by means of wire bonding. The light-emitting diode abounds in luminance and excels in electrostatic breakdown voltage.

Ionization in strong electric fields and dynamics of nanosecond-pulse plasmas

Abstract: The paper describes experimental and computational studies of air plasmas sustained by high repetition rate high-voltage nanosecond pulses. Current and voltage measurements, together with earlier microwave diagnostics, allowed us to determine the efficiency of ionization. The energy cost per newly produced electron in these diffuse volumetric plasmas was found to be on the order of 100 eV, two orders of magnitude lower than in diffuse quasineutral DC and RF plasmas, and comparable with or even lower than in the cathode sheaths of glow discharges. A plasma kinetic model was developed and tested against the experimental Paschen breakdown curve in argon. The kinetic model was found to adequately describe the Paschen curve, and the important role of ionization by fast ions and atoms near the cathode, as well as the increase in secondary emission coefficient in strong fields described in the literature, was confirmed. Modeling of plasma dynamics in highvoltage nanosecond pulses yielded the energy cost of ionization, which was found to agree well with the experimental values. Both experiments and modeling revealed that the ionization cost per electron in these plasmas is relatively insensitive to the gas density. Detailed investigations of the plasma dynamics revealed a critical role of the cathode sheath that was found to take up most of the peak voltage applied to the electrodes. The extremely high E/N, much higher than the Stoletov’s field at the Paschen minimum point, results in a very high ionization cost in the sheath. In contrast, the E/N in the quasineutral plasma is closer to that associated with the Stoletov’s point, resulting in a near-optimal electron generation. This behavior (the reversal of ionization efficiencies in the sheath and in the plasma) is opposite to that in conventional glow discharges. The positive space charge in the sheath and its relatively slow relaxation due to the low ion mobility was also found to result in reversal of electric field direction in the plasma at the tail of the high-voltage pulse.

Influences of Electrical Conductivity of Wall on Magnetohydrodynamic Control of Aerodynamic Heating

Abstract: Influences of the electrical conductivity of the wall of a space vehicle on the control of the aerodynamic heating in Earth-reentry flight by applying the magnetic field are numerically examined using an axisymmetric two-dimensional (r-z) thermochemical nonequilibrium magnetohydrodynamic computational fluid dynamics code. Numerical results show that when the wall of an axisymmetric blunt body is assumed to be an insulating wall, applying a dipole-type magnetic field with r and z components pushes the bow shock wave away from the blunt body and reduces the aerodynamic heating. On the other hand, when the wall is assumed to be a conducting wall, the aerodynamic heating cannot be reduced by applying the magnetic field. This is because the strong Hall electric field on the r-z plane cannot be obtained in the case of the conducting wall, so that the large electric current density in the azimuthal direction cannot be obtained and the shock wave cannot be pushed away from the blunt body.

Electrical-prospecting method for hydrocarbon search using the induced-polarization effect

Abstract: We propose a method of surface and marine electrical prospecting using controlled-source excitation. The method is designed to detect hydrocarbon deposits at depths of a few kilometers and to map their boundaries. The technique is based on imaging the induced-polarization (IP) parameters of the geologic formation. We use the fact that, because of the imaginary part of the electric conductivity, polarized media support wave propagation processes whose nature is similar to displacement currents induced by the dielectric permittivity. However, unlike displacement currents, these processes reveal themselves at much lower frequencies and, therefore, at greater depths. It is established that the ratio of the second and the first differences of the electric potential does not decay after the current turn-off in polarized media, whereas it decays quickly if the IP effect is absent. Thus, the IP response can be observed directly and separated from the electromagnetic (EM) response. We use a vertical focusing of the electric current to decrease the effect of laterally adjacent formations to apply a 1D layered model in a 3D environment. This method obtained promising results in several regions of Russia.